1. Field of the Invention
The invention relates to the field of preparation and storage of ready-to-use liquid for renal therapy. The invention relates in particular to a bag system for preparing and holding fresh and spent dialysis liquid. In addition, one subject of the invention is a multi-chamber bag for holding concentrates and for preparing a medical solution of the concentrates, as well as a method for preparing a medical solution from several concentrates.
2. Description of the Related Art
Renally insufficient patients suffer from restricted kidney function which prevents the required elimination of substances that are eliminated in the urine from the patient's body. For these patients, toxic metabolites must be removed by purifying their blood in a dialysis treatment.
In dialysis, the blood is purified via a mass exchange membrane which comes in contact with the patient's blood on one side and with a cleaning liquid on the other side. The cleaning liquid is a so-called dialysis solution which receives the substances intended for separation and conveys them out of the patient's blood. Dialysis solutions in general consist of an aqueous composition of physiologically important dissolved components, for example, electrolytes, buffers and osmotically active reagents such as glucose.
In peritoneal dialysis (PD), the dialysis solution is infused into the peritoneum of the patient. The patient's peritoneum serves as a mass exchange membrane through which the blood is purified. In the course of treatment or toward the end of treatment the peritoneum is emptied and the dialysis solution is discarded.
In hemodialysis (HD) the patient's blood to be purified is passed through an extracorporeal blood circulation and brought in contact with an artificial mass exchange membrane. The opposite of the mass exchange membrane is brought in contact with dialysis solution, so that substances which pass through the membrane can be removed from the blood by crossing the membrane with the dialysis solution.
In cases of both HD and PD dialysis the dialysis solutions contain typical dissolved substances such as:                Electrolytes Na, K, Mg, Ca to maintain an acceptable electrolyte balance in the patient        Buffers (for example, bicarbonate, acetate, lactate, etc.)        Glucose (or other osmotic agents) as osmotic agents in peritoneal dialysis or to maintain the blood sugar level during hemodialysis        Acids or salts of acids (for example, HCl and/or chloride, acetic acid and/or acetate, citric acid and/or citrate) which may contribute toward neutralization of basic partial dialysis solutions or are present as counterions in the electrochemical equilibrium.        
In hemodialysis, partial solutions or partial concentrates are often mixed in the dialysis machine before and during the course of the treatment in preparing a finished dialysis solution. Partial concentrates in solid or liquid form are frequently used for this. These are held in individual containers and are diluted by connection to the dialysis machine with the help of a prepared hydraulic system, then are mixed and prepared to yield the ready-to-use dialysis solution.
In another variant, dialysis solutions are prepared in a batch in a step preceding the treatment. The batch is stored in a tank that has been prepared for being connected to a dialysis machine. In many cases, the tank is an integral component of a dialysis treatment unit. In other embodiments, the dialysis tank is separate from the treatment station and is designed to be functionally mobile. The use of a tank with dialysis liquid may thus offer the advantage of being able to select the treatment site to be relatively independent of the location by one-time preparation of the dialysis liquid. Treatment stations at different locations can thus be used without having to rely on a preparation unit for dialysis solution or a water connection to supply the water needed to dilute the concentrates. In these cases, the dialysis solution is mixed from concentrates on an equipment unit provided for this purpose and then is stored, usually in a mobile tank.
In addition, there are known container systems whose ready-to-use solution is placed in a container and this container, e.g., as an inner bag is enclosed by another container. Such concepts are known from beverage technology in particular and are described as “bag in a box” systems, among others.
Systems that have been developed further in the field of dialysis therapy are systems in which the inner container holds the ready-to-use liquid and the container surrounding the inner vessel is prepared for receiving the spent liquid. The inner vessel is then surrounded by the spent liquid in the outer container.
U.S. Pat. No. 4,386,634 describes a container system for preparing a ready-to-use solution for hemodialysis. The ready-to-use solution is prepared in a film bag having a large inner volume by dissolving concentrates. The inner bag is surrounded by water in the outer container.
DE 195 10 759 describes a container system consisting of an inner film bag of a large volume and a flexurally rigid container surrounding the inner bag. The ready-to-use dialysis liquid is placed in the inner bag first and the spent liquid is filled into the space between the inner bag and the outer surrounding container.
WO 2011/073274 describes a bag system with an inner bag and an outer bag surrounding the inner bag. The dialysis liquid is prepared by dissolving the concentrates in the inner bag. Spent dialysis liquid is filled into the space between the inner bag and the outer bag. The entire bag system may additionally be inserted into a flexurally rigid supporting apparatus.
The inner flexible container in the container systems described in the state of the art can have a negative influence on the flow conditions in the outer container due to the development of folds or due to the fact that its position in the space of the surrounding container is not fixed. In particular the inner bag may cover the incoming flow area of the outer container, so that incoming spent liquid is prevented from entering the outer container. In addition, the mobile inner bag may prevent the incoming spent liquid from being uniformly distributed in the outer container. It is possible that initially only portions of the outer container are filled with the oncoming flow of spent liquid. Due to the growing hydrostatic pressure, the inner bag may be displaced suddenly, resulting in an equally sudden equalization of flow in the outer container, which may lead to unacceptable vibrations of the entire apparatus and unacceptably high stress on the material.
A first measure which can prevent excessive mobility of the inner bag in the outer container has already been described in WO 2011/073274 in which it is disclosed that the edges of the inner bag may be welded to the edges of the surrounding bag along a welding line. The inner bag is secured in the outer bag around the circumference in this way. However, it has been found that this measure is also inadequate for achieving uniform filling of the outer container.
The object was therefore to refine a container system for the production and/or storage of ready-to-use liquids or spent liquids with an inner bag and a container surrounding the inner bag so that when liquid is supplied to the outer container, a good equalization of flow is created, so that the container is uniformly filled with an increase in the filling.